Conduct a 4th examination of the NHLBI twin study from participants at the Indiana Center. All subjects are male, born between 1917 and 1927 and were previously seen from 1 to 3 times since 1972-73. Major elements of Exam 4 are to study the relationship between cardiovascular disease risk factors collected over the three preceding exams, changes in cognitive function since Exam 3 in 1986-87, and brain morphology and aging assessed by magnetic resonance imaging. Objectives are to evaluate prospective relationships of CVD risk factors and indices of brain morphology at Exam 4, determine the extent of difference in MRI profiles in twin-pairs discordant for hypertension and diabetes and CVD, characterize changes in neuropsychological performance from Exam 3 to Exam 4, determine heritability of new measures obtained from MRI, and study the complex relationship between CVD risk factors and cognitive decline and brain aging in older twins.